The invention relates in general to respiratory protective masks and in particular to a new and useful control for a protective mask.
Respiratory apparatus with excess pressure in the interior of the mask make sure that a higher pressure relative to the ambience is maintained in the mask during both the exhalation and the inhalation. This excess pressure prevents the ambient atmosphere which might be noxious from penetrating into the mask in use. Even with a leak, the gas flows from the inside outwardly. However, in masks of this kind, difficulties are met in that after use, upon removing the mask and thus opening the respiratory circuit, the breathing gas supply must be stopped or the function of the lung demand valve reversed, since otherwise breathing gas flows out unused and the service time of the apparatus is reduced.
A prior art respiratory mask is equipped with a lung demand valve producing and maintaining an excess pressure in the interior of the mask. The housing of this valve accommodates a respiratory chamber to be placed in front of the user's respiratory ducts and an outer chamber communicating with the outer atmosphere, and a pressure chamber therebetween which is connected to each of the adjacent chambers by a valve. This pressure chamber produces an excess pressure in the respiratory chamber, and thus in the interior of the mask, during both the inhalation and the exhalation. For this purpose one wall of the pressure chamber is movably connected to the inner wall of the valve housing through a control diaphragm. An actuating chamber caused by the respiration to a respiratory gas inlet valve of the mask.
A reversible locking mechanism makes it possible to interrupt the respiratory gas supply upon removing the mask. The locking mechanism includes a shaft which is mounted for rotation in the respiratory chamber. One end extends in an airtight bushing through the wall of the respiratory chamber to the outside where it is provided with a radial actuating lever permitting the pivoting of the shaft between two end positions. In one of the end positions, the locking position, a resilient lug of the actuating lever engages a recess in the wall of the respiratory chamber. In the interior, the shaft carries a wire strap. In the locking position, the wire strap engages the lever arm of the inlet valve and holds the valve in its closed position. A spring clip urges the wire strap, which is pivotable along with the shaft, into the other end position, the release position, in which the strap applies against the inside of the respiratory chamber and does not obstruct the free movement of the lever arm. With the mask removed, the actuating lever is engaged in its locking position whereby the breathing gas supply is interrupted. Upon putting the mask on, the first inhalation starts an automatic operation. During this operation, the suction acting on the diaphragm during the inhalation must produce a force acting on the lever arm and being sufficient for disengaging the locking mechanism. The spring clip brings the locking mechanism into the release position (German OS No. 30 38 100).
Since the force determining the setting in operation depends on engaging elements of the locking mechanism provided at the outside, the respective resistance of the elements to engagement and thus the reliability of the mechanism may be affected in the course of time by soiling, mechanical damages, or wear. The airtight bushing in the wall of the respiratory chamber is expensive and potentially a source of trouble, and so are the many individual parts of which the locking mechanism is assembled.
Another prior art lung demand respiratory apparatus, operated with compressed air and providing an excess pressure in the protective mask comprises a control diaphragm in the lung demand, and a metering valve to be opened by a preliminary pressure. The control diaphragm is exposed to the pressure of the ambient air and bounds a control space in the interior which is under the pressure of the interior of the mask. The control diaphragm is connected through a rocker arm to the metering valve to close it against the action of the inflowing compressed air as soon as a certain excess pressure is reached in the control space. A lengthwise movable spacer pin is tightly passed from the control space to the outside through the wall opposite the control diaphragm. The pin applies in the control space against a stop plate which is spring loaded in the direction of the control diaphragm. On its outer end, the spacer pin carries a rotatable reversing lever having the shape of an eccentric and bearing against the wall of the control space. In its position with the eccentric released, which is the locking position, the stop plate applies against the locker arm. The force of the compression spring then closes the metering valve even if the protective mask is removed and thus no excess pressure is present in the control space. In the position with the eccentric tensioned, which is the release position, the stop plate is held spaced from the locker arm and the control diaphragm is free to move. The reversal to the release position is automatic and occurs as soon as under the first breath the control diaphragm of the rocker arm displaces the spacer pin against the spring action outwardly. The reversal lever which is thereby unloaded is so oriented relative to the gravity that it tips into the release position under the weight of its handle. The reversal into the locking position is effected manually (German OS No. 26 20 170).
A precondition for the automatic release is that at that instant, the user remains in a position ensuring the provided orientation relative to the gravitational direction. Otherwise this reversal must also be effected manually. The necessary sealing of the space pin in the wall of the control space is expensive and susceptible to disturbances.
Still another prior art pressure gas protective apparatus provides an excess pressure in the mask which is connected through a lung demand valve and a line to the outlet of a pressure reducer wherefrom it is supplied with breathing gas.
Within the lung demand valve, a control diaphragm is exposed on its outside to the ambient pressure and loaded by a spring. The inside is loaded by the pressure in the interior of the mask. Against this side, one arm of a pivoted rocker arm is applied, while the other arm thereof is connected to the closing member of the valve, namely a piston. The closing piston is provided with a transverse aperture through which, in a respective position, the breathing gas line is either connected to the interior of the mask, or shut off. The following operating positions may be considered:
1. In standby position, with the mask removed, the interior of the mask is under the ambient pressure. The spring on the diaphragm is relieved and displaces through the rocker arm the closing piston into an end position thereby closing the breating gas line.
2. With the mask put on, upon an exhalation, an excess pressure is built up. Through the diaphragm, which bears against the spring, and through the rocker arm, the closing piston is displaced into the open position. Breathing gas flows into the mask. Upon reaching the desired excess pressure in the interior, the closing piston is displaced into the other end position and again interrupts the breathing gas supply.
3. During the further inhalation, the excess pressure is reduced; the desired excess pressure is maintained by a subsequent control of the closing piston.
4. Upon removing the mask, the excess pressure dissipates. The motion of the diaphragm displaces the closing piston into the other end position, the breathing gas flow is interrupted and the standby position as under 1 is reached again (German Pat. No. 30 15 760).
This prior apparatus with an excess pressure in the protective mask is suitable for being used under normal conditions. Conditions which require sudden greater amounts of breathing gas supply or even involve dynamic stresses, for example due to a run or jumps, cause jerky movements of the closing piston and thus uncontrolled respiratory conditions in the interior of the mask.